Low temperature high flash point turbine engine fuel

ABSTRACT

A turbine engine fuel having a high flash point and low viscosity at -60*F comprising a blend of two to twenty percent by volume of a C10 or higher alkyl benzene and the remaining volume consisting of a hydrogenated naphtha oil fraction. The fraction is obtained by taking a naptha fraction from the crude and hydrogenating the naptha fraction to reduce aromatics. Aromatics containing ten or more carbon atoms are then added to the naptha fraction.

United States Patent Nestor Oct. 28, 1975 LOW TEMPERATURE HIGH FLASH POINT TURBINE ENGINE FUEL Inventor: Leonard J. Nestor, Philadelphia, Pa.

Assignee: The United States of America as represented by the Secretary of the Navy, Washington, DC.

Filed: Nov. 28, 1973 Appl. No.: 419,565

US. Cl. 60/208 Int. Cl. C06D 5/00 Field of Search 60/208, 39.02, 39.06;

References Cited UNITED STATES PATENTS 10/1963 Stahly 44/80 3,177,653 4/1965 Barnes et al. 60/208 Primary Examiner-Samuel Feinberg Attorney, Agent, or FirmR.. S. Sciascia; Henry Hansen [57] ABSTRACT A turbine engine fuel having a high flash point and low viscosity at -60F comprising a blend of two to twenty percent by volume of a C or higher alkyl benzene and the remaining volume consisting of a hydrogenated naphtha oil fraction. The fraction is obtained by taking a naptha fraction from the crude and hydrogenating the naptha fraction to reduce aromatics. Aromatics containing ten or more carbon atoms are then added to the naptha fraction.

8 Claims, No Drawings LOW TEMPERATURE HIGH FLASH POINT TURBINE ENGINE FUEL STATEMENT OF GOVERNMENT INTEREST The invention described herein may 'be manufac tured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION Thisinvention relates generally to the field of fuels and more particularly to a turbine engine fuel having a high flash point and low viscosity.

In developing a fuel for a new Naval missile, called a Harpoon missile, propelled by a gas turbine engine and launched from carrier based Naval aircraft, two fuel property characteristics are essential. Since the missiles are stored aboard Naval vessels, safety regulations require that the fuel have a flash point in excess of 140F. Engine specifications further require that the fuel have a' viscosity less than 12 centistokes at -60F to allow the engineto start at high altitudes. Exhaustive surveys made of available fuels indicate that the first two requirements could not be met by existing known percent by volume of a hyrdrogenated naptha oil fraction, and a C or higher alkyl benzene comprising from 2 to percent by volume of the combination of the solvent and the alkyl benzene, the blended fuel having a flash point in excess of 140F and a maximum viscosity of 12 centistokes at 60F.

DESCRIPTION OF THE PREFERRED EMBODIMENT A general physical property rule for fuels is the higher the flash point the higher the viscosity. It is further recognized that a fuel having the desired properties could be produced by blending pure compounds or by using narrow cut fractions of selected jet fuels. However, these approaches are not only complex and difficult to implement, but they also involve extraordinary expense. Since naphthenes tend to have comparatively low viscosities, a survey of products derived from high napthenic crudes discloses several solvents that have good freeze points, comparatively low viscosities at low temperatures and high flash points. Three such solvents are Kerr Magee Corporation Napoleum 140 solvent, Ashland Chemical Company. 140 solvent, and Union Oil Company Amsco 140 solvent, all of whose properfuels. Neither JP-4 nor JP-S type fuels, commonly in ties are listed in Table 1.

TABLE 1 NAPOLEUM ASHLAND AMSCO PROPERTY 140 140 140 TEST METHOD API Gravity at 60F 45.7 46.5 49.6 D-287 Specific Gravity at 60F 0.7985 0.7949 0.781 Pounds Per Gallon at 60F 6.648 6.62 6.51 Color. Saybolt +30 +30 D-l56 Flash Point, F. TCC I 142 142 D-56 Kauri-Butanol Value 35 37.1 30 0-1 133 Araline Point, F 145 138.2 164 D-l0l2 Distillation. "F V D-86 Initial Boiling Point 372 368 366- 10% 376 372 374 380 375 380 90% 389 380 393 Dry Point 400 386 405 End Point 405 390 406 Composition Volume 7:

Parafins 48.4 55.2 53 Mass Spectroscopy Olefins 0.3 Napthenes 47.7 35.4 47 Mass Spectroscopy Aromatics 3 9 9.1 l D-l 319 Refractive Index at 77F 1.4405 D-l2l8 Heat of Combustion-FIA-BTUILB. 18,660 Sulfur, PEM l D-l266 Acidity of Distillation Neutral D-l093 Residue 2A IA 1A D-l30 Corrosion-During Distillation Indicates ASTM Test Procedure use for gas turbine engines, meet the necessary requirements. JP-4 fuel, which has a relatively low viscosity at low temperatures, has a flash point below 140F, and JP-S fuel, which has a flash point about 140F and is ap provedfor Navel use, has a viscosity in excess of engine requirements at F. 1 i

SUMMARY OF THE INVENTION Accordingly, it is a general purpose and object of the present invention to provide a relatively inexpensive I fuel suitable for use in a gas turbine engine, and having a flash point in excess of 140F and a viscosity less than 12 centistokes at -60F.

These and other objects are accomplished according to the present invention by a blended fuel consisting essentially of a parafinic solvent containing at least 35 As noted in the table, these solvents contain at least 35% naphthenes and 48% parafins.

To support the applicability of high naphthenic crudes to fill the present fuel requirements of the Harpoon missile, a routine sample of of JP-S fuel was also required in the .lP-S fuel specification used by-,the .Na y- Y Temperature-viscosity relationships of alkyl benzenes reveal them to be ideally suited as blending agents in order to achieve the desired fuel properties. The relationship between total number of carbon atoms of the alkyl benzenes, and their respective flash points is such that only alkyl benzenes having at least ten total carbon atoms (C will satisfy the flash point requirement of 140F or higher. However, pure C s are relatively expensive, ranging in price from $10 per gallon to $l per gallon. The least expensiveC is secondary butyl benzene costing approximately per gallon. In order to keep fuel cost down and remain within a 25% aromatic content limitation, blending was deemed desirable.

ln' testin'g various combinations of pure materials, several 'fuels meeting the desired requirements were obtainedfiThe following examples are presented for purposes of illustration and not of limitation.

I I EXAMPLE 1 I "A composition of fuel comprising 80% by volume of Ashland 140 solvent blended with %by volume of secondary butyl benzene (one of a group of C" alkyl benzenes) was produced using standard blending techniques. The blended fuel had a flash point of 142F (determined by ASTM D-93 Test Procedure) and a viscosity of 10.6 centistokesat 60F (determined by ASTM D-445 Test Procedure). Sea level starting tests were conducted a't'low temperatures using the present blend of fuel on an AiResearch model GTC 85-1 16 auxilliary power unit (APU), which has a gas turbine engine similar to that used in the Harpoon missile. Sea level starting of'the. APU was achieved at an ambient temperature of-64F (viscosity l 1.8 centistokes). In comparison tests with JP-4 fuel it was determined that the time required to attain idle speed of the APU was slightly less with the present blended fuel.

EXAMPLE 2 "'A c om posi'tion of fuel comprising 98% by volume of Napoleum 140 blended with 2% by volume of seconda'ry butyl. benzene was produced as in Example 1. The

a blended fuel had a flash point of 152F, and a viscosity of 12.0 centistokes at 60F determined as in Example 1. Starting tests with theAPU yielded results similar to Example 1.

EXAMPLE 3 EXAMPLE 4 A composition offuel comprising 87% by volume of Amsco 140 solvent blended with 13% by volume of secondary butyl benzene was produced as in Example 1. The blended fuel had a flash point of 152F, and a .viscosity of 12.0 centistokes-at 60F determined. as in Example 1. Starting .tests with the APU yielded results i similar to. Example l.'

4 Studies made with otherypureC alkyl benzenes, such as iso butyl benzene and norrnal butyl benzene, indicates that blending them with any of the solvents disclosed herein would yield successful results similar to those reported in Examples l-4. This conclu- "sion is based upon carefulcomparison of their porperthan 12 centistokes at 60F,'making them suitable for use in a gas turbine engine operating in extremely low environmental temperatures. The blended fuels further possess the desirable property of having flash points in excess. of 140F, making them safe for storage aboard naval vessels. Heretofore, these properties have been deemed inconsistent with each other and unavailable in a relatively inexpensive fuel.

Obviously,,many modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is: l. A blended fuel suitable for turbine engines consisting essentially of:

a parafinic solvent containing at least 35 percent by volume of a hydrogenated naphtha oil fraction; and an alkylbenzene having at least 10 carbon atoms comprising from 2 to 20 percent by volume of the combination of said solvent and said alkyl benzene, selected from the group consisting of secondary butyl benzene, iso butyl benzene and normal butyl benzene 4 whereby the blended fuel has a flash point in excess of 140F and a maximum viscosity of 12 centistokes at '60"F. 2. A fuel as set forth in claim 1 wherein said alkyl benzene is secondary butyl benzene.

3. A fuel as set forth in claim l-wherein said alkyl benzene is iso butyl benzene.

4. A fuel as set forth in claim 1 wherein said alkyl benzene is normal butyl benzene.

5. The process of operating a gas turbine engine which comprises the steps of:

feeding a mixture "or air and a fuel consisting essentially of a parafinic solvent containing at least 35 percent by volume of a hydrogenated naphtha oil fraction; and an alkyl benzene having at least 10 carbon atoms comprising from 2 to 20 percent by volume of the combination of said solvent and said alkyl benzene, selected from the .group consisting of secondary butyl benzene, iso butyl benzene and normal butylb'enzene', the blended fuel having a flash point inexc'ess of"! 40F and a maximum viscosity of 12 ceritistokes at 60F,"to a 'chamber; subjec'ting'said mixture to'comb'ustion'; passing the resulting hot combustion gases through a turbine to partially expand the gases therein; and discharging the hot gases into the atmosphere through a nozzle to produce thrust." 6. A process asset" forth in claim 5 wherein said alkyl benzene is secondarybutyl benzene.

7. A process as set forth in claim 5 wherein said alkyl benzene is iso butyl benzene. i

8. A process asset forth in claim 5 wherein said alkyl benzene is normal butyl benzene- 

1. A BLENDED FUEL SUITABLE FOR TURBINE ENGINES CONSISTING ESSENTIALLY OF: A PARAFINIC SOLVENT CONTAINING AT LEAST 35 PERCENT BY VOLUME OF A HYDROGENATED NAPHTHA OIL FRACTION, AND AN ALKYL BENZENE HAVING AT LEAST 10 CARBON ATOMS COMPRISING FROM 2 TO 20 PERCENT BY VOLUME OF THE COMBINATION OF SAID SOLVENT AND SAID ALKYL BENZENE, SELECTED FROM THE GROUP CONSISTING OF SECONDARY BUTYL BENZENE, ISO BUTYL BENZENE AND NORMAL BUTYL BENZENE, WHEREBY THE BLENDED FUEL HAS A FLASH POINT IN EXCESS OF 140*F AND A MAXIMUM VICOSITY OF 12 CENTISLOKES AT -60*F.
 2. A fuel as set forth in claim 1 wherein said alkyl benzene is secondary butyl benzene.
 3. A fuel as set forth in claim 1 wherein said alkyl benzene is iso butyl benzene.
 4. A fuel as set forth in claim 1 wherein said alkyl benzene is normal butyl benzene.
 5. The process of operating a gas turbine engine which comprises the steps of: feeding a mixture of air and a fuel consisting essentially of a parafinic solvent containing at least 35 percent by volume of a hydrogenated naphtha oil fraction, and an alkyl benzene having at least 10 carbon atoms comprising from 2 to 20 percent by volume of the combination of said solvent and said alkyl benzene, selected from the group consisting of secondary butyl benzene, iso butyl benzene and normal butyl benzene, the blended fuel having a flash point in excess of 140*F and a maximum viscosity of 12 centistokes at -60*F, to a chamber; subjecting said mixture to combustion; passing the resulting hot combustion gases through a turbine to partially expand the gases therein; and discharging the hot gases into the atmosphere through a nozzle to produce thrust.
 6. A process as set forth in claim 5 wherein said alkyl benzene is secondary butyl benzene.
 7. A process as set forth in claim 5 wherein said alkyl benzene is iso butyl benzene.
 8. A process as set forth in claim 5 wherein said alkyl benzene is normal butyl benzene. 